The present application is the U.S. national stage application of International Application PCT/EP00/01513, filed Feb. 24, 2000, which international application was published on Sep. 14, 2000 as International Publication WO 00/53962 in the English language. The International Application claims priority of Luxembourg Patent Application 90367, filed Mar. 5, 1999.
The present invention relates to a gas cylinder valve and more particularly to a gas cylinder valve with a diaphragm member for use with high and ultra high purity gases.
Gas cylinder valves are used to seal and to control the discharge of gas from gas cylinders. In some applications, the gas dispensed from the gas cylinder must remain free of impurities. This is especially true in the semiconductor industry where any impurities in the gas can adversely affect the electrical properties of the device and can greatly decrease the manufacturing yield. Most often these gases are also very corrosive and toxic.
Commonly, the valves used for high purity, ultra high purity and/or highly corrosive or toxic gases are diaphragm valves. Such diaphragm valves are e.g. disclosed in U.S. Pat. Nos. 5,516,078 or 5,823,509. They include a valve body having a valve chamber, an inlet passage and an outlet passage therein. The inlet passage communicates via a seat with the valve chamber. An obturating body is arranged in the valve chamber and is movable relative to the valve seat. A valve stem is connected to the obturating body for moving the latter between a closed position, wherein the obturating body sits on its valve seat so as to seal gas discharge through the valve, and an open position, wherein the obturating body is spaced from the valve seat so as to allow gas discharge from the gas cylinder through the valve seat. A diaphragm member forms a flexible wall of the valve chamber opposite the valve seat. It forms a sealing separation between the valve chamber and a stem chamber in which the valve stem is housed. The valve stem, the obturating body and the diaphragm member are fused together, so that a reciprocating movement of the valve stem elastically deforms the diaphragm member.
It will be noted that the outlet passage of the above valves is in direct communication with the valve chamber, so that ambient air humidity may enter the latter when the valve is closed. This air humidity may condense in the valve chamber. If a corrosive gas is then discharged through the valve chamber, the condensate accumulated therein will inevitably form strong acids in the valve chamber. These strong acids might attack for example the diaphragm member in the valve chamber.
It will also be noted that the above valves are usually used with gas cylinders under high pressure. It follows that high closing forces are required for maintaining the obturating body in a sealed position on its seat and to open it.
DE-A-859,583 discloses a gas valve designed for flow control functions requiring a low-setting control. It includes a valve housing having a valve chamber, an inlet passage and an outlet passage communicating with the valve chamber. A valve disk is biased by a closing spring onto a first valve seat, which is located between the valve chamber and the outlet passage. The valve chamber is consequently under gas pressure when the valve is closed. A valve body is located in the valve chamber and associated therein with a second valve seat. An axial bore connects the first valve seat to the second valve seat. The valve body is loosely connected to the valve disk via a hollow valve shaft extending through the axial bore, so that it is axially spaced from the second seat when the valve disk sits on the first seat. A metal membrane forms a gastight separation wall between the valve chamber and an outer actuating shaft. The latter is capable of axially pushing via the membrane onto the valve body. In a first step, the actuating shaft pushes the valve disk via the valve body and the hollow valve shaft axially away from the first valve seat. Over the second valve seat a high gas flow establishes into the hollow shaft and then over the first valve seat in to the outlet passage. In a second step the actuating shaft pushes the valve body onto the second valve seat. Now a reduced gas flow establishes through a flow restricting nozzle in the valve body into the hollow shaft and then over the first valve seat in to the outlet passage. When the actuating shaft does not axially push via the membrane onto the valve body, then the closing spring pushes the valve disk onto the first valve seat and closes the valve. It will be noted that when the valve is closed, the closing spring has to warrant that gas pressure acting onto the valve disk seated on the first valve seat does not open the valve.
There is a need for an improved gas cylinder valve in which the diaphragm member is better protected against corrosion and which requires lower closing forces to maintain the obturating body in a sealed position on its seat and to open it.
A gas cylinder valve in accordance with the invention comprises a valve body having a valve chamber, an inlet passage and an outlet passage therein. The inlet passage and the outlet passage communicate with the valve chamber. An obturating body is movable relative to a valve seat in the valve body. A valve stem is connected to the obturating body for moving the latter between a closed position, wherein the obturating body sits on the valve seat so as to seal gas discharge through the valve seat, and an open position, wherein the obturating body is spaced from the valve seat so as to allow gas discharge from the gas cylinder through the valve seat. A first diaphragm member forms a flexible wall of the valve chamber. This first diaphragm member is mechanically connected to the valve stem, so that a reciprocating movement of the valve stem elastically deforms the first diaphragm member. In accordance with an important aspect of the invention, the valve seat is located between the valve chamber and the outlet passage. The inlet passage is in direct pressure communication with the valve chamber, so that the valve chamber is under gas cylinder pressure when the valve is closed. The obturating body is arranged, in the direction of the discharged gas, downstream of the valve seat, so that the gas cylinder pressure acting on the first diaphragm member in the valve chamber tends to pull the obturating body on its valve seat. It will first be appreciated thatxe2x80x94when the valve is closedxe2x80x94the valve chamber containing the first diaphragm member is sealed by the obturating body relative to the outlet connection. It follows that ambient air humidity cannot enter into the valve chamber an condense on the first diaphragm member. It will further be appreciated thatxe2x80x94when the valve is closedxe2x80x94the valve chamber containing the first diaphragm member is in pressure communication with the interior of the gas cylinder. It follows that the gas cylinder pressure acts on the first diaphragm member and contributes to the closing force maintaining the obturating body on its seat.
In a preferred embodiment the cross-section sealed in the valve chamber by the first diaphragm member is bigger than the cross-section sealed by the obturating body sitting on its seat. It follows thatxe2x80x94when the valve is closedxe2x80x94a positive pressure force will press the obturating body on its seat.
A preferred embodiment of the valve has furthermore one ore more of the following features. The stem extends axially through the first diaphragm member, wherein a gas tight weld advantageously provides a gasproof connection between the stem and the first diaphragm member. The valve body has a stem chamber with a shoulder therein, wherein the first diaphragm member lies with its outer edge on the shoulder and is advantageously connected thereto by means of a gasproof weld. The valve may further include a second diaphragm member axially spaced from the first diaphragm member in the stem chamber. In this case, a channel in the valve body will advantageously allow to create a partial vacuum in the stem chamber between the first and second diaphragm member, so as to be able to check whether the latter still provide the required gas tightness.
The valve has advantageously a sealing cap with an integrated locking device for pushing the obturating body firmly against its seat, when the sealing cap is put onto the outlet connection.
The outlet passage is advantageously housed in an outlet connection that is removably fixed to the valve body.
In a preferred embodiment, the valve further includes an linear actuator. This linear actuator is then advantageously mounted on the valve body and connected to the valve stem by means of a lever mechanism. The latter is preferably mounted outside of the valve body laterally thereof. It includes for example a lever arm connected by means of an articulation to an actuating rod of the actuator, and an intermediate articulation for the lever arm on the valve body. This lever arm has a free end bearing against a bearing surface on a tip of the valve stem, so as to be able to push the valve stem into the valve body.
A preferred embodiment of the valve body includes: a flange for mounting the valve on a gas cylinder; a relatively thin neck having most of the inlet passage therein; and a first transverse body supported by the relatively thin neck. The first transverse body has the valve chamber and the seat and the outlet passage therein. It is housing the obturating body, the valve stem and the first diaphragm member; wherein the axis of motion of the stem is transverse to the relatively thin neck. The valve body may further include a second transverse body supported on the first transverse body. This second transverse body then houses a linear actuator, as for example a pneumatic cylinder, wherein the axis of motion of the linear actuator too is transverse to the relatively thin neck.